A so-called stator-type sector plate is formed as a large wheel centered on an upright axis and with a multiplicity of axially throughgoing passages that are angularly and radially separate and that are packed with heat-storing plates or the like constituting the thermal mass of the system. Upper and lower hoods are fitted over the upper and lower axially directed faces of this plate to subdivide the air flows through the plate so that the different streams can pass through the various passages, even in different directions.
In my earlier German patent application No. 2,162,248 published June 20, 1973 a system is disclosed where the hoods are of butterfly shape in axial projection, each being formed by two diametrically opposite 90.degree. segments. These hoods are rotated together so that hot exhaust gases can flow through half of the segments in one direction while cooler combustion gases are flowed in the opposite direction. Periodically the hoods are stepped angularly to change the alignment and allow the heated thermal mass or matrix to give off its heat to the combustion gases. As a rule the hoods are journaled on a post fixed in the center of the stator, and carry seals closely juxtaposed with the respective faces thereof.
Such arrangements are quite large, often having a diameter of more than 8 m. The extremes in temperature between the two faces of the plate can therefore account for axial movements of more than 50 mm, cupping the entire sector plate so that its entry side is convex and its exit side is concave. This has the effect of raising the core or center of the plate in the standard situation where the hot air flows down through the sector plate. As a result the upper hood, which is carried like the lower hood on a post fixed in the center of the sector plate, is lifted relative to the upper face and can leave quite a gap at the outer edge of the plate while the outer edges of the plate move toward the lower hood. The standard sliding seal urged by springs against the surface it is sealing cannot normally compensate for such displacements. Thus seal arrangements must be provided that can resist the enormous heat encountered while not inhibiting motion between the plate and the structure facing it.
Various complex systems have been suggested to reduce this leakage. Forming the support frame for the thermal mass of a plurality of concentric spaced rings, as described in German Pat. No. 1,237,150 filed Oct. 3, 1964 by H. Brandt, has been found to reduce the deformation somewhat. The deformation is corrected right at the seals in the system of German patent document No. 2,205,838 filed Feb. 8, 1972 by E. Puritz, wherein thermal bilayer bars that bend greatly when heated act through lever mechanisms on the seals to cancel out the effect of the sector-plate deformation on them. A thermally actuated seal arrangement for a sector plate is seen in U.S. Pat. No. 3,246,687 of A. Jensen et al.
Other systems employ complex metallic bellows-type seals and just let the sector plate deform. Such means can compensate to a limited extent, but do not eliminate the deleterious effects of the thermal deformation of the sector plate. Similarly suspending the seals from supports on the bearing housing has proven an equally problem-filled method of accommodating to the thermal-deformation problem.
None of these arrangements operates easily. They all require complex mechanical arrangements or actions in a structure that is subject to enormous temperature variations. Making any mechanism work in such circumstances is difficult, as its pieces are as subject to thermal deformation as the sector plate they are to act on.